title: Biomechanical evaluation of a metal-on-metal cervical intervertebral disc prosthesis.
abstract: BACKGROUND
  In vitro nondestructive flexibility testing of the CerviCore total disc replacement (TDR) was performed. It was hypothesized that TDR would not significantly alter biomechanics relative to intact, whereas rigid fixation would cause significant changes.
  
  
  OBJECTIVE
  To assess the ability of a cervical metal-on-metal saddle-shaped TDR to replicate normal biomechanics in vitro.
  
  
  METHODS
  Human cadaveric flexibility experiment.
  
  
  METHODS
  Nine human cadaveric C3-T1 specimens were tested intact, after TDR and after anterior plating. Flexion, extension, lateral bending, and axial rotation were induced by pure moments; flexion-extension was then repeated using a simplified muscle force model with 70-N follower load. Optical markers measured three-dimensional intervertebral motion, and eight points of laminar surface strain were recorded near the left and right C5-C6 facet joints. Biomechanical parameters studied included range of motion (ROM), lax zone (LZ), angular coupling pattern, sagittal instantaneous axis of rotation (IAR), and facet loads normal to the facet joint plane. Mean values of parameters were compared statistically using repeated measures analysis of variance and Holm-Sidak tests.
  
  
  RESULTS
  Total disc replacement caused significant reduction in ROM during extension (p=.004) and significant reduction in LZ during lateral bending (p=.01). However, plating significantly reduced both ROM and LZ during flexion, extension, and lateral bending (p<.006). Sagittal IAR shifted relative to intact by 3.6 mm after TDR (p>.05) and 6.5 mm after plating (p>.05). Coupled axial rotation/degree lateral bending was 99% of intact after TDR but 76% of intact after plating (p=.15). Coupled lateral bending/degree axial rotation was 95% of intact after TDR but 85% of intact after plating (p=.43). Neither construct altered facet loads from intact.
  
  
  CONCLUSIONS
  With regard to ROM, LZ, IAR, and coupling, deviations from intact biomechanics were less substantial after TDR than after plating. Facet load alterations were minimal with either construct. Our results show that this particular TDR permits ROM and maintains some measures of kinematics in a cadaver model.
authors.affiliation: Regional Brain & Spine, LLC, 1723 Broadway, Suite 410, Cape Girardeau, MO 63701, USA.
authors.forename: Kyle O
authors.initials: KO
authors.lastname: Colle
authors.forename: John B
authors.initials: JB
authors.lastname: Butler
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Reyes
authors.forename: Anna G U S
authors.initials: AG
authors.lastname: Newcomb
authors.forename: Nicholas
authors.initials: N
authors.lastname: Theodore
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology; D002574:Cervical Vertebrae / Q000601:surgery*; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D008422:Materials Testing; D019736:Prostheses and Implants; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D059145:Total Disc Replacement; D016474:Weight-Bearing / Q000502:physiology
keywords: Artificial disc; Biomechanics; Cervical arthroplasty; Kinematics